Dear Renuka,

welcome,

I will give you a conceptual answer and then you implement the solution.

The first step is sample and digitalize audio signal. It seems that the file is a stored audio file in the computer so it is already sampled and digitized.

This means every sample has an n-bit format. In the end effect you have an audio stream of 0nes and zeros. This is the starting point of modulating these digital data. In four QAM according to the constellation of the 4 QAM you have 4 possible symbols:

S0, with logic values 00 and S0= 1/sqroot 2 ( -1, - j)

S1, with logic values 01 and S1= 1/sqroot 2 ( -1, +j)

S2 with logic values 10 and S2 = 1/sqroot 2 (1, -j)

S3 with logic value 11 and S3= 1/sqroot 2 (1,+j),

So one has two channels the real I channel and the imaginary Q channel.

every symbol contains two bits, so you encode every two bits according to the table given above. That is you have two sequences the I sequence and the Q sequence.

Best wishes

First we need to quantize the analog signal By ADC. This is in my book (The American University Laboratories For Electrical Engineering Part 1).

At this point we have a stream of ones and zeros.

It is time to do modulation. Let us say we have a carrier A cos (wt)

00 A cos(wt+45)

10 A cos(wt+135)

11 A cos(wt+225)

01 A cos(wt-45)

This is 4 points QAM.

You will find Proakis book (Digital Communications) a very good one for this question.

Aparna Sathya Murthy, thank you for your response, any file in dot wave (.wav) format

Abdelhalim Zekry SIr, thank you very much for the response, my doubt is how to convert a audio file in dot wave format to digital data i.e series of '0', '1' s, after that to 4-QAM using Matlab.